This study uses EEG to study brain waves at rest and in response to specific auditory and visual sensory stimuli in autistic children. We hypothesize that, compared to same age peers, autistics will show abnormalities in their electrophysiologic processing of sounds (tones and phonemes)and visual stimuli (flashes of light)and that these abnormalities will be able to separate autistics not only from typical children but also into clinical subgroups with specific biological/electrophysiological characteristics. We hope to find biological measures which will prove diagnostic of autism in very young children and which can be used in the measurement of treatment outcome in future intervention trials.